The present invention relates to articulation mechanisms for vehicle seats.
More particularly, the invention concerns an articulation mechanism for a vehicle seat, intended to connect two components belonging to the seat and pivotally mounted relative to each other around an axis of rotation, said articulation mechanism comprising:
first and second cheek webs intended to be fixed respectively to the two seat components, these cheek webs being pivotally mounted relative to each other around said axis of rotation, the second cheek web being fixed in a permanent way with a tooth portion which extends over at least a circular arc centered on the axis of rotation,
several locking inserts each fitted with a tooth portion suitable to engage with the tooth portion of the second cheek web, each locking insert being movable relative to the first cheek web between an engagement position where the tooth portion of the locking insert engages with the tooth portion of the second cheek web to lock the articulation mechanism, and a withdrawn position where the locking insert does not engage with said tooth portion of the second cheek web,
a cam to control the movement of the locking inserts, this cam comprising first, second and third support edges projecting outwards and distributed angularly around the axis of rotation, the third support edge of the cam making with the first and second support edges respective angles greater than 100 degrees, the cam being pivotally mounted around the axis of rotation and being acted upon by resilient means towards an angular off-position where the support edges of said cam place the locking inserts in their engagement position, and the cam being movable by a user to an angular operational position where said cam allows the locking inserts to move to their withdrawn position,
and disengagement means adapted to place the locking inserts in their withdrawn position when the cam is in its operational position.
The above-mentioned disengagement means can be constituted particularly by one or more of the following means:
a pivoting insert fitted with cam edges engaging with a part of the locking inserts,
one or more springs,
the forms of the teeth of the tooth portion of the second cheek web and of the locking inserts, which forms are then adapted to make the inserts slide radially inwards as soon as the two cheek webs rotate relative to each other when the first cam is in its operational position, etc.
Document EP-A-0 720 930 describes an example of such an articulation mechanism, intended to allow the adjustment of the angular position of the back of the seat relative to the seat part. This articulation mechanism comprises three locking inserts distributed angularly at 120 degrees from each other.
The articulation mechanism described in this document gives complete satisfaction, but the inventors of the present invention have wanted to improve on it still further, by making it lighter and less expensive.
To this end, according to the invention, an articulation mechanism of the type in question is essentially characterised in that the locking inserts are two in number and engage with the first and second support edges of the cam, and in that said locking mechanism comprises additionally a stop which is integral with the first cheek web and which is arranged so that the third support edge of the cam is supported radially on said stop when the cam is in its off-position, the third support edge of the cam making with the first and second support edges respective angles greater than 100 degrees such that the stop can exert on the cam a radial reaction adapted to counterbalance radial stresses exerted by the locking inserts on the cam when a pivoting torque is applied between the first and second cheek webs.
By means of these arrangements, an articulation mechanism is obtained which has a breaking strength comparable to the three-insert mechanisms of the prior art, while being lighter and less expensive on account of the elimination of one insert.
Moreover, the interior fitting of the articulation mechanism according to the invention is in the main identical to that of the three-insert mechanisms of the prior art, which makes it possible:
to retain in large part the manufacturing and assembly tools previously used for three-insert mechanisms,
and/or to use these tools alternately to make three-insert mechanisms or two-insert mechanisms according to the invention, which brings an increase in flexibility to the manufacturing process.
These advantages help still further to reduce the cost price of the articulation mechanism according to the invention.
Lastly, the internal fitting of the articulation mechanism according to the invention makes it possible to release a part of the internal space between the first and second cheek webs, a space which can be used beneficially to add functionalities to the articulation mechanism.
In particular, this free space can be used to add to the articulation mechanism an angular position memorisation device similar to the one described for example in French patent application no. 97-13 702, intended to allow a vehicle seat back to be folded down in order to give access to the places in the rear of this vehicle, then for the back to be returned to its original angular position.
In preferred embodiments of the invention, it may be possible to use additionally one and/or other of the following arrangements:
the third support edge of the cam makes with the first and second support edges respective angles near to 120 degrees;
the first and second support edges of the cam each engage with a rear end belonging to one of the inserts and the stop is arranged approximately at the same distance from the axis of rotation as said rear ends of the locking inserts when these inserts are in the engagement position;
the first cheek web comprises at least one support area which is in permanent radial contact with the second cheek web, approximately without clearance, this support area being arranged near the locking inserts to take up radial stresses exerted by these locking inserts on the second cheek web when a pivoting torque is applied between the first and second cheek webs;
the first cheek web comprises two support areas which are each in permanent radial contact with the second cheek web, approximately without clearance, each support area being arranged in relation to one of the locking inserts;
the locking inserts are arranged so that, when they are in the engagement position, each tooth of each insert is supported against one face of the tooth portion of the second cheek web which is facing the stop.